Phase change ink based marking systems or ink jet printing systems are well known in the art. In some of these systems, an imaging surface or roller is positioned in an operative relationship with a print head. In embodiments solid inks are used whereby a final receiving surface or print medium is brought into contact with the imaging surface after the image has been placed thereon by the print head. The image is then transferred and fixed to the final receiving surface by the imaging member in combination with a transfix pressure member. This process begins by first applying a thin liquid or release agent such as silicone oil to the imaging medium or member surface. The present embodiments of this invention are concerned with replacing this silicone oil release agent in an ink jet or transfix system with a substantially improved release agent comprising a poly-alpha olefin.
Ink jet printing systems of the type disclosed herein are described in U.S. Pat. Nos. 4,538,156; 5,502,476; 5,389,958 and 6,196,675.
Generally, a solid or phase change ink jet marking comprises: a source of ink; one or more print heads each having at least one ink jet for discharging droplets of ink; a transfer or imaging medium or member having a moving surface adjacent to but spaced apart from the jet of each print head; circuitry for controlling the print head to project droplets of ink onto the imaging medium to create patterns of droplets thereon, and an arrangement for transferring the droplets from the imaging or transfer medium to paper or another printing medium. If not all of the ink or oil is transferred to the printing medium, it is necessary to clean the imaging medium prior to the time that new indicia are placed thereon. Actually, the imaging member in these types of systems have a dual function; first the ink jet print heads prints images on the imaging member; thus, it is used as an imaging member, secondly, after receiving the images, the image is then transfixed to a final print medium, so this member provides a transfix function in addition to an imaging function.
The proper release agents are important in these types of systems to improve diffusion into the paper bulk more readily than the currently practiced polyorganisiloxanes. These silicone oils interact with the surface of both coated and un-coated paper stocks resulting in a thick layer of this remaining on these surfaces. The thin layer of release oils on surface of the images adversely affects the customer end use applications which include the ability to write on the surface, post it notes adhesion, bookbinding, etc. This results in significant customer dissatisfaction.
The use of polymeric release agents having functional groups which interact with a marking component to form a thermally stable, renewable self-cleaning layer having good release properties for electroscopic thermoplastic resin toners are described in, for example, U.S. Pat. Nos. 4,029,827, 4,101,686 and 4,185,140, the disclosures of each of which are totally incorporated herein by reference.
In ink jet marking systems and subsystems, silicone fluids are presently predominantly used as release agents. There are many associated defects and failure modes associated with the use of these fluids, especially when they are employed in machines printing full colors and requiring longer service life. Functional silicone oils are by nature chemically and physically susceptible to reaction with many other species in the environment, such as inks and ink additives, ink components, components of the paper, etc. Side reactions with these species can lead to premature gelation, ink offset slime, image defects, which ultimately lead to shortened component and subsystem operation life. This life shortfall directly impacts operation costs incurred by both manufacturers and customers. As earlier noted, end use applications in particular are negatively impacted by the use of amine-functional silicone fluids, as the amine functionality interacts with the surface of both coated and un-coated paper stocks. This leaves a persistent film on the surface that inhibits adhesives, US overcoats write-ability, post-it notes use, book binding, and other end use elements from properly functioning. Low viscosity polydimethyl siloxane (PDMS) improves Solid ink jet print quality in many areas, but cannot be lowered any further due to limitations of volatility in low viscosity silicone fluids. PAO may provide similar benefits as low viscosity (10 cP) silicone, but at higher viscosities, thus at a lower volatility. This is based on the fact that silicone fluids are slightly miscible with phase change inks, and PAO fluids are more miscible with phase change inks.